Modern refrigerator appliances use a gas-based refrigerant to provide cooling for the fresh food and/or freezer compartment of the refrigerator. The refrigerant is circulated within a loop that includes passage through the inside compartment(s) of the refrigerator. Heat is withdrawn from inside the refrigerator by changing state from a liquid to a gas in an evaporator. Thereafter, the refrigerant is compressed and subsequently cooled by passage through a heat exchanger—more commonly referred to as a condenser. The condenser is typically exposed to ambient air for heat exchange therewith.
In order to improve efficiency, refrigerators can provide heat exchange between the relatively cool refrigerant vapor conveyed from the evaporator outlet through the suction line to the compressor and the relatively warm liquid refrigerant conveyed from the condenser outlet through the capillary tube to the evaporator inlet. This heat exchange improves the thermodynamic efficiency of the refrigeration system by cooling liquid refrigerant before it enters the evaporator. Because the cold gaseous refrigerant passing through the suction line is warmed to at least ambient temperature as it passes from within the insulated space of the refrigerator to the compressor inlet, the residual refrigeration effect of the cold suction line gas might otherwise be wasted if not used to cool the warmer liquid refrigerant exiting the condenser. The heat exchange technique between gaseous and liquid refrigerant is sometimes termed “suction-capillary tube heat exchange.”
Several techniques can be used for placing the suction line and capillary tube into thermal contact for heat exchange therebetween. By way of example, one technique includes affixing the capillary tube to the outside of the suction line. Another technique for providing a suction line/capillary tube assembly for heat exchange is to pass the capillary tube inside the suction line in heat exchange relationship with the gaseous refrigerant passing therethrough. This is sometimes termed a “coaxial” heat exchange, although actually the capillary tube is not necessarily precisely centered within the suction line. The capillary tube may even contact the interior surface of the suction line at random points. As used herein, suction-capillary tube heat exchanger refers to these and other assemblies where the suction line and capillary tube are placed into thermal contact with each other for heat exchange therebetween.
Using either technique, the suction-capillary tube heat exchanger can be placed e.g., within the foamed-in insulation of a refrigerator located between the outer case and the inner liner forming the interior of the refrigerator or otherwise encased in a foam sleeve and positioned along an exterior of the refrigerator. By insulating the heat exchanger, more heat can be efficiently transferred from the capillary tube to the suction line rather having the suction line absorb heat from the environment, which would necessarily reduce its capacity to absorb heat from refrigerant in the capillary tube.
Similarly, to further improve efficiency, it is desirable to insulate the cold suction line as it leaves the evaporator in order to maintain its relatively cooler temperature before reaching the compressor or the suction line/capillary tube heat exchanger. In addition, for certain applications, it is likewise desirable to insulate the capillary tube coming from the condenser. For example, it may be necessary to route the capillary tube through the machinery compartment after the condenser. Because the machinery compartment can be relatively warm due to the compressor, insulation may be required. Again, for either the suction line or the capillary tube, foam insulation may be used.
However, there can be certain drawbacks to the use of foam insulation—whether such is wrapped around an element or such element is placed in the foam between the outer and inner liner. For example, foam is an imperfect insulator that will still allow for a certain amount of heat transfer. In addition, if the foam becomes wet due to e.g., condensation, the insulation ability of the foam is decreased and becomes worse as the amount of condensation in or on the foam increases. For instance, condensation can occur when the foam is cooled below the dew point by the refrigerant in the suction line to the compressor.
Accordingly, an insulator that provides for improved thermal efficiency in insulating portions of the refrigeration cycle of a refrigerator appliance would be useful. Such an insulator that can be readily installed either along the exterior of refrigerator or in the space between the outer case and the inner liner would also be beneficial. An insulator that can reduce the operating costs of a refrigerator by improving the refrigerator's thermal efficiency would also be very useful.